Diabetes mellitus is a syndrome characterized by abnormal insulin production, increased urinary output and elevated blood glucose levels. There are two major subclasses of diabetes mellitus. One is the insulin-dependent diabetes mellitus (IDDM or Type I), formerly referred to as juvenile onset diabetes since it was evident early in life, and non-insulin dependent diabetes mellitus (NIDDM or Type II), often referred to as maturity-onset diabetes. Exogenous insulin by injection is used clinically to control diabetes but suffers from several drawbacks. Insulin is a protein and thus cannot be taken orally due to digestion and degradation but must be injected. It is not always possible to attain good control of blood sugar levels by insulin administration. Insulin resistance sometimes occurs requiring much higher doses of insulin than normal. Another shortcoming of insulin is that while it may control hormonal abnormalities, it does not always prevent the occurrence of complications such as neuropathy, retinopathy, glomerulosclerosis, or cardiovascular disorders.
Orally effective antihyperglycemic agents are used to reduce blood glucose levels and to reduce damage to the nervous, retinal, renal or vascular systems through mechanisms affecting glucose metabolism. Such agents act in a variety of different mechanisms including inhibition of fatty acid oxidation, a-glycosidase inhibition, antagonism of a.sub.2 -receptors and inhibition of gluconeogenesis. Two classes of compounds have predominated: the biguanides as represented by phenformin and the sulfonylureas as represented by tolbutamide (Orinase.RTM.). A third class of compounds which has shown antihyperglycemic activity are thiazolidinediones of which ciglitazone is the prototype. Ciglitazone suppresses the symptoms of diabetes--hyperglycemia, hypertriglyceridemia and hyperinsulinemia [Diabetes 32, 804-10 (1983)]. Rezulin, a member of the thiazolidinediones, has recently been used successfully in the treatment of type II diabetes mellitus. ##STR4##